Seltzer water is plain water that has been infused with carbon dioxide gas under pressure. That’s it: two ingredients, water and CO2. When you crack open a can or bottle, the pressure drops and the dissolved gas escapes as the familiar stream of bubbles. The process is surprisingly simple, and understanding it also helps explain why seltzer sits in a category of its own compared to club soda, tonic water, and sparkling mineral water.
How Carbonation Works
Carbon dioxide dissolves more easily in cold water under high pressure. Seltzer manufacturers chill filtered water and then force CO2 into it inside a sealed tank or bottle. The gas dissolves into the liquid, forming carbonic acid, a weak acid that gives seltzer its slightly tart, crisp taste. As long as the container stays sealed, the CO2 stays dissolved. Once you open it, the pressure equalizes with the atmosphere and the gas starts escaping as bubbles.
The amount of carbonation varies by brand. More CO2 means smaller, more aggressive bubbles and a sharper bite on your tongue. Less CO2 produces a gentler, softer fizz. That sensation you feel isn’t just the bubbles popping, either. The carbonic acid actually activates pain receptors on your tongue, which is why flat seltzer tastes noticeably different from the same water when it was fizzy. Your brain interprets that mild sting as part of the refreshing quality.
What Makes Seltzer Different From Other Sparkling Waters
The sparkling water aisle can be confusing because several products look identical but are made differently.
- Seltzer water is filtered water plus carbon dioxide. Nothing else is added. It’s the simplest form of carbonated water.
- Club soda starts the same way but includes added minerals like sodium bicarbonate, potassium sulfate, or sodium citrate. These give it a slightly salty, mineral flavor that some people prefer in cocktails.
- Sparkling mineral water (like Perrier or San Pellegrino) comes from a natural spring and contains minerals from the source. Some are naturally carbonated underground; others have CO2 added after bottling. The mineral content gives each brand a distinct taste.
- Tonic water contains quinine, sweeteners, and sometimes citric acid. It has significant calories and sugar, unlike the others on this list.
If you’re looking for the cleanest option with no additives, seltzer is the one. The ingredient list on a can of plain seltzer reads: carbonated water. That’s the entire list.
How Seltzer Is Made at Home
Home carbonation machines like SodaStream work on the same principle as commercial production, just at a smaller scale. A pressurized canister of food-grade CO2 connects to the machine. You fill a bottle with cold water, attach it, and press a button that forces gas into the water. More presses mean more carbonation. The whole process takes about 10 seconds.
Cold water is key. Water at refrigerator temperature (around 35 to 40°F) absorbs significantly more CO2 than room-temperature water. If you try to carbonate warm water, you’ll use more gas, get fewer bubbles, and the fizz will go flat faster. Most home carbonation guides recommend chilling your water for at least an hour before carbonating.
You can also carbonate water with a simple DIY setup using a CO2 tank, a regulator, and a length of food-safe tubing, which is how many homebrewers and bartenders do it. The concept is identical: pressurize cold water with CO2 in a sealed container.
Does Seltzer Affect Your Health?
One of the most common concerns is whether the carbonic acid in seltzer damages tooth enamel. Plain seltzer has a pH of roughly 3 to 4, making it more acidic than still water (pH 7) but far less acidic than soda (pH 2 to 3) or orange juice. Studies on carbonated water and dental erosion generally find that plain seltzer poses minimal risk to enamel compared to sugary or citrus-flavored drinks. Flavored seltzers with added citric acid are more erosive, so if dental health is a concern, plain is the safer choice.
Another common question is whether seltzer causes bloating or digestive issues. The CO2 does introduce gas into your digestive system, and some people notice bloating or burping, especially if they drink it quickly. For most people this is mild and temporary. Some research actually suggests carbonated water can help with indigestion and constipation, though the evidence is limited.
From a hydration standpoint, seltzer hydrates you exactly as well as still water. The carbonation doesn’t reduce your body’s ability to absorb the water. If drinking seltzer helps you consume more fluids throughout the day, it’s doing its job.
Why Seltzer Tastes Different Across Brands
Even though seltzer is technically just water and CO2, brands taste noticeably different. Three factors explain this. First, the source water matters. Municipal tap water, spring water, and reverse-osmosis purified water all have different baseline mineral profiles that affect flavor. Second, carbonation levels vary. A brand that pumps in more CO2 will taste sharper and more acidic. Third, the size and speed of the bubbles differ based on how the carbonation is done and how long it’s held under pressure before packaging.
Flavored seltzers add another layer. Most use “natural flavors,” which are typically essential oils or fruit extracts added in very small amounts. These contain no sugar, calories, or sweeteners in most cases, but they do change the acidity and mouthfeel. Citrus-flavored varieties tend to be the most acidic because citrus oils naturally contain acids that compound with the carbonic acid already present.